A typical prior art head and disk system 10 is illustrated in FIG. 1. In operation the magnetic transducer 20 is supported by the suspension 13 as it flies above the disk 16. The magnetic transducer 20, usually called a “head” or “slider,” is composed of elements that perform the task of writing magnetic transitions (the write head 23) and reading the magnetic transitions (the read head 12). The electrical signals to and from the read and write heads 12, 23 travel along conductive paths (leads) 14A, 14B, 15A, 15B which are attached to or embedded in the suspension 13. The magnetic transducer 20 is positioned over points at varying radial distances from the center of the disk 16 to read and write circular tracks (not shown). The disk 16 is attached to a spindle 18 that is driven by a spindle motor 24 to rotate the disk 16. The disk 16 comprises a substrate 26 on which a plurality of thin films 21 are deposited. The thin films 21 include ferromagnetic material in which the write head 23 records the magnetic transitions in which information is encoded. The thin film protective layer (not shown in FIG. 1) is typically the last or outermost layer.
The conventional disk 16 typically has a substrate 26 of AIMg or glass. The thin films 21 on the disk 16 typically include a chromium or chromium alloy underlayer that is deposited on the substrate 26. The magnetic layer in the thin films 21 is based on various alloys of cobalt, nickel and iron. For example, a commonly used alloy is CoPtCr. However, additional elements such as tantalum and boron are often used in the magnetic alloy.
FIG. 2 illustrates one common internal structure of thin films 21 on disk 16. The protective overcoat layer 37 is used to improve wearability and corrosion. The materials and/or compositions which are optimized for one performance characteristic of an overcoat are rarely optimized for others. The most commonly used protective layer materials for commercial thin film disks have been carbon, hydrogenated carbon (CHx), nitrogenated carbon (CNx) and CNxHy. Efforts to optimize overcoat properties have included use of a layer structure using different materials and/or compositions for each of two or more layers in the overcoat structure. For example, U.S. Pat. No. 5,942,317 issued to R. White describes the use of a graded CHx protective layer wherein the hydrogen content is highest at the film's surface to take advantage of the lower polar surface energy characteristic of higher hydrogen levels (which improves corrosion resistance) and is lowest at the interface with the magnetic layer to optimize the adhesion properties. The midlevel of the CHx film is likewise optimized by having an intermediate hydrogen concentration which has a high hardness to improve wearability. The variations in the hydrogen content can be continuous or discrete. For example, a protective layer structure with three sublayers with lower hydrogen concentration nearest the magnetic layer, intermediate hydrogen concentration in the middle sublayer and high hydrogen concentration at the surface is suggested in White '317. Hardness and density are reduced by the presence of hydrogen in certain percentage ranges; thus, the overcoat structure of White '317 is hardest and densest at the interface with the magnetic layer.
In U.S. Pat No. 5,679,431 Chen, et al., describe the use of a bilayer protective overcoat in which the initial sublayer is carbon, titanium or chromium and the surface sublayer is CHx or CNx. The problem being addressed in Chen '431 is diffusion of nitrogen or hydrogen into the magnetic layer over time. The initial sublayer is intended to act as a diffusion barrier.
U.S. Pat. No. 6,086,730 to Liu, et al., describes a method for sputtering a carbon protective layer with a high sp3 content which involves applying relatively high voltage pulses to the carbon target. Liu '730 asserts that the resulting carbon overcoat has good durability and corrosion resistance down to low thicknesses.
In order to improve the performance of magnetic thin film media the protective overcoat 37 must be made as thin as possible to reduce the separation from the magnetic transducer 20 and the magnetic thin film 33 while maintaining the protective function.